On Mon, Aug 19, 2019 at 8:06 PM John Darrington <j...@darrington.wattle.id.au> wrote: > > On Mon, Aug 19, 2019 at 10:07:11AM -0500, Segher Boessenkool wrote: > > > ? As I remember there were a few other ideas from Richard Biener and > > Segher Boessenkool.? I also proposed to add a new address register > which > > will be always a fixed stack memory slot at the end. Unfortunately I am > > not familiar with the target and the port to say in details how to do > > it.? But I think it is worth to try. > > The m68hc11 port used the fake Z register approach, and I believe it had > some special machine pass to get rid of it right before assembler output. > > (r171302 is when it was removed -- last version was > > https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/config/m68hc11/m68hc11.c;h=1e414102c3f1fed985e4fb8db7954342e965190b;hb=bae8bb65d842d7ffefe990c1f0ac004491f3c105#l4061 > for the machine reorg stuff). > > No idea how well it works... But it's only needed if you are forced to > have a frame pointer IIUC? > > > Segher > > > Most of these suggestions involve adding some sort of virtual registers > So I hacked the machine description to add two new registers Z1 and Z2 > with the same mode as X and Y. > > Obviously the assembler balks at this. However the compiler still > ICEs at the same place as before. > > So this suggests that our original diagnosis, viz: there are not enough > address registers was not accurate, and in fact there is some other > problem?
That sounds likely. Given you have indirect addressing you could simulate N virtual regs by placing them in a virtual reg table in memory and accessed via a fixed address register (assuming all instructions that would need an address reg also can take that indirect from memory). Richard. > J' > > -- > Avoid eavesdropping. Send strong encrypted email. > PGP Public key ID: 1024D/2DE827B3 > fingerprint = 8797 A26D 0854 2EAB 0285 A290 8A67 719C 2DE8 27B3 > See http://sks-keyservers.net or any PGP keyserver for public key. >